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The adrenal medulla and paraganglia are part of the autonomic/sympathetic nervous system. The endocrine and nervous systems are alike in that they exert their actions by releasing hormones/neurotransmitters that bind to cell surface receptors in the target tissue, thereby inducing an effect.

Autonomic nerves are not under conscious control. They innervate the heart, adrenal medulla, vascular smooth muscle, and smooth muscle in visceral organs, thereby controlling cardiac rate and output, adrenal medullary secretion of catecholamines, blood pressure, the genitourinary tract, and intestinal motility. Autonomic nerves originate within the central nervous system and have two major divisions according to their anatomic locations:

(1) Parasympathetic preganglionic nerves exit the central nervous system via the cranial nerves and sacral spinal nerves. They terminate in nonchromaffin paraganglia that are most numerous in the neck and associated with the glossopharyngeal and vagus nerves. These ganglia serve as chemoreceptors that are involved in the control of respiration. An important paraganglion at the carotid bifurcation is known as the carotid body. They are also found along the jugular vein and in the jugulo-tympanic region. Head-neck paragangliomas are tumors that arise from these parasympathetic paraganglia.

(2) Sympathetic preganglionic nerves exit the central nervous system via the thoracic and lumbar spinal nerves. The sympathetic nervous system coordinates the body's automatic fight-flight response by stimulating the adrenal medulla to secrete catecholamines and by directly stimulating cardiac output and blood flow to muscles while diverting blood flow away from visceral organs.

Sympathetic preganglionic nerves terminate mainly in paravertebral and prevertebral nerve ganglia where they secrete acetylcholine as their neurotransmitter; they are, therefore, known as cholinergic nerves. These nerve ganglia are collectively known as paraganglia and contain neuroendocrine cells that are similar to adrenal medullary cells on light microscopy by chromaffin and immunohistochemical staining. Paraganglia are also found in the mediastinum, particularly adjacent to the cardiac atria, and in the abdomen along the sympathetic nerve chains in paravertebral and prevertebral positions. Paraganglia are plentiful along the aorta, particularly around the celiac axis, adrenal glands, renal medullae, and aortic bifurcation (organ of Zuckerkandl). ...

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